Blender 2.8 Transform stretch problem
Looks like you've got Proportional Editing turned on - you might have accidentally activated it with the hotkey O, or by clicking the small blue circle button just above the timeline, a little to the right of center. You can turn it off by pressing O or clicking the button again. That should restore the behavior you're used to.

That being said, proportional editing can be a really useful tool, so if you're not familiar with it, I'd definitely recommend reading up on it!